This application claims the benefit of Korean Patent Application Nos. 2003-34390 and 2003-43997 filed on May 30, 2003 and Jun. 30, 2003, which are hereby incorporated by reference for all purposes as if fully set forth herein.
1. Field of the Invention
The present invention relates to a color cathode ray tube, and in particular to a color cathode ray tube capable of satisfying drop requirements and preventing partial doming and howling by adjusting an inner curvature radius and/or a difference of height of a cathode ray tube panel.
2. Description of the Prior Art
In general, a color cathode ray tube (hereinafter CRT) displays images, and it is divided into two types of CRT: a curved-surface CRT and a flat CRT.
Because the curved-surface CRT has problems such as image distortion and light reflection, demand therefore has decreased gradually. On the other hand, because the flat CRT can prevent image distortion and light reflection and implement the maximum visible light region, demand therefore has gradually increased.
FIG. 1 is a side view illustrating a general color CRT. The conventional color CRT includes: a panel 1 having an effective surface on which a phosphor screen a is coated; a mask 2 disposed with a predetermined interval to the inner side of the panel 1; a funnel 3 combined with a rear of the panel 1 in order to maintain the inside of the CRT as a vacuum state; and a deflection yoke 5 for deflecting electron beams emitted from the electron gun 4.
In the above-mentioned conventional color CRT, when the electron gun 4 receives an image signal, the electron gun 4 emits an electron beam, and the emitted electron beam is accelerated and focused toward the panel 1 by a voltage applied to each electrode of the electron gun 4. The electron beam is deflected by the deflection yoke 5, color selecting is performed while the electron beams passes a slot (not shown) formed in the mask, and each phosphor screen is irradiated by the electron beam landing on the phosphor screen 1a at the internal surface of the panel 1.
In order to satisfy the demand for lower price, lower weight, and slimmer color CRTs, methods for tinting a panel, using a cheap AK mask, increasing/decreasing a center thickness of a panel and flattening the panel have been used. In case of reducing a center thickness of a panel, when a center thickness of a panel is less than the regulation value (it is regulated so as to be greater than 10.5 mm), X-Ray release is increased, and accordingly there is a limitation to the minimum center thickness of the panel. In the panel flattening method, because the internal surface of a panel is gradually flattened, the internal curvature of a mask is gradually decreased, reducing the structural strength of the mask, and accordingly the drop characteristics (drop quality) of the mask decrease.
As described above, when the structural strength and the drop characteristics of the mask deteriorate, because of heat expansion of the mask, an electron beam passing a mask hole can not accurately hit the red, blue, or green phosphor on the screen, the color purity of the screen deteriorates, and accordingly partial doming and howling occur.
As described-above, in a conventional color CRT, particularly in a color CRT smaller than 21″, in order to satisfy the structural strength and drop requirements of the mask, the wedge ratio of the panel (thickness ratio of a corner portion to the central portion of the screen) is determined so as to be not less than 220%, the inner curvature radius of the mask is uniformly maintained, and a mask thickness is determined so as to be not less than 0.13 mm. Accordingly, it is impossible to lower a price, obtain slimness and reduce weight of a CRT and meet the above requirements.